The present embodiments relate to an add-on unit for an object table of a mammography device for positioning a patient breast during an X-ray exposure.
Female breast tissue may be screened for carcinoma development using X-ray radiation.
Owing to the particular anatomical characteristics of a region of the body that is being examined, specialized devices (e.g., mammography units) are used for the examination using X-rays.
Exposure settings of the mammography devices have evolved into standard settings for diagnostic purposes. The following two standard settings may be used:
A medio-lateral oblique (MLO) view of the breast (e.g., MLO projection) is the default setting in early breast cancer detection mammography. In this case, the breast is imaged at a 45° angle. The 45° oblique view may visualize outer upper quadrants, axillary tails and inframammary folds.
A cranio-caudal view of the breast (e.g., CC projection) may be acquired vertically from above. The CC projection may show as much breast tissue as possible and may visualize all breast segments with the exception of breast segments located furthest away laterally and axillarily.
In the course of a standard examination, 2-plane mammography may be performed. The 2-plane mammography combines the medio-lateral oblique (MLO) and the cranio-caudal (CC) views.
Mammography devices may have an object table or a lower plate, on which the breast to be imaged is placed. The breast may be compressed with the aid of a compression plate pressing onto the breast from above (e.g., the breast is clamped between the compression plate and the object table).
Good compression results in mammographic images having improved image resolution, image definition and contrast.
By reducing the breast thicknesses to be penetrated by the radiation, compression also leads to a significant dose reduction in the glandular tissue.
In the case of MLO exposures, the 45° position of the compressed breast may be unpleasant for the patient. Positioning small women (for oblique projections) on digital mammography devices having a large full field digital mammography (FFDM) of 24×30 cm, for example, causes problems. The problem of MLO positioning in the case of small women with smaller breasts is less critical with small detectors having a recording area of, for example, 18×24 cm.
In order to make the exposure easier for the patient, movable compression plates (e.g., “shift paddles”) have been introduced. The mode of operation of a movable compression plate is shown in FIG. 2. A breast 10 that is to be examined is compressed using an object table 1 and a movable compression plate 2. The movable compression plate 2 is movably mounted on a retaining fixture 3 such that the movable compression plate 2 is displaceable substantially vertically with respect to the beam path. The displacement directions are indicated by the arrow 12. The retaining fixture 3 is mounted on a stand (not shown) so as to be tillable together with the object table 1. The 45° angle for the MLO exposure may be set by tilting the retaining fixture 3. This is illustrated in the figure by the ray beam 5 shown, which forms an angle of approximately 45° with the vertical. The ray beam 5 is collimated using a collimator 4.
In FIG. 2, the compressed breast 10 is positioned at an edge of the object table 1 in order to permit the arm 11 of the patient to be placed next to the object table 1. For this asymmetric positioning of the breast 10 in relation to the object table 1, the compression plate 2 is moved in the direction of a right-hand edge of the object table 1. In order to record an image of a region of the object table 1, in which the breast 10 is placed, the ray beam 5 is directed onto the region by a corresponding adjustment of the collimator 4. This may also be referred to as an asymmetric collimation, because the ray beam 5 is not directed centrally onto the object table 1.